基于CCD拼接的航空相机小波自动调焦方法研究

An Automatic Wavelet Focusing Method of the Aerial Camera Based on CCD Mosaicing

为精确地进行航空相机调焦,获取高清晰度的航空影像,结合CCD拼接的特点,提出一种新的航空相机调焦方法,便于航空成像设备进行自动调焦。考虑人类视觉系统的特点设置权值,利用图像的小波分解系数构造清晰度评价函数;分析小波基函数的性质,对不同频率成分的影像进行清晰度评价,从而使评价函数对图像的变化具有适应性,通过比较得出了利用symlet2小波进行3层分解获得的评价函数的效果最佳。为了提高清晰度评价函数的灵敏度,选取了细节丰富的区域作为评价区域,详细地阐述了航空相机利用CCD拼接结构的特点进行调焦的算法实现过程。试验证明,该方法获得的评价函数比传统的小波方法灵敏度高,可以满足航空相机的需要,大大提高了地物目标的识别和提取的精度。

In order to eraluate the image obtained by the aerial camera more clarely,a focusing method which could auto-focus was proposed to consider the characteristic of the mosaicing structure.The evaluation function has taken the characteristic of the human vision system（HVS） into account to set the weights,and is constructed by the wavelet coefficients of the image.For the sake of making the function suit to different images,the properties of the wavelet basis were analyzed.By comparing the evaluating effect of different images,the wavelet basis with the best effect was symlet2 and the level of decomposing was three.Meanwhile,the area with high frequency component was chosen as the evaluation area in order to improve the sensitivity of the evaluation function.In this paper,the flow chart of the focusing based on this method was described particularly.The simulation result showed that the evaluation function obtained by this method is more sensitive and adaptive than the traditional wavelet methods.It could acquire high image quality,and meet the application in focusing system of the aerial camera to improve the objects identification precision.